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RFID tag measurements

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inpinj tag

Lets try to understand our requirement.

We have an antenna which is non 50 ohms , say R+J x ohms which needs to be matched to a chip of ipedance R1-Jx ohms. (we need to make R equal to R1, but its difficult in some cases)

Now our measuring system is 50 ohms calibrated, say network analyser.We can match this in 2 ways ,
1. calibrate and make netwok analyser impedance to R ohms , and i think that is not possible
2. so only solution is match the antenna impedance to 50 ohms using known elements (LC matching)and take measurement, back calculate antenna impedance replacing 50 ohms (on a smith chart) with chip impedance.

Also for measuring tag antenna you may require a probe of low pitch , may be a Wafer probe.

:D I think i am wrong, confused......


Any other method, any comments on this pls.....


regards
GV
 

cst backscattering

i have done read the CST rfid example.
in the material, it is said that Simulation of the planar structure with a standard 50 Ωport and then add matching network.
and in the practical application,the IC impedance is R+jx..so,the matching network is not fit here.

Now,my problem is how to measure the antenna impedance without IC,in order to validate my simulation.

regards.
ZY.
 

rfid antenna measurement

Ok. Lets try for experimental. have you got any vector network analyser? if you have, you get a result applying probe to asic nodes of tag antenna. if you dont have any find a VSWR meter and find VSWR. after that you have to use below equations;

VSWR=1+|Γ| / 1-|Γ| and Γ=Zin-Z0 /Zin+Z0

Z0.. characteristic impedance of feed line (actually 50)
Γ... measure of reflected signal at feed point.


Zin ll be your result.



refer link for:

**broken link removed**
 

how to tell if rfid tag is gone

Thanks zirtapoz. the Doc is useful.
 

rfid micro measurement

hi zirtapoz
.i cant open the site.. my net is restricted i guess ....
would you pleased post it as postscript here.

however,i am still comfused about the RFID antenna impedance measurement.
as: 1.how to get VSWR?in UHF band,the common probe isnot accurate anymore.
2.the antenna is printed on PET,i think normal way for measurement isn't suitable here.

..more and more comfused... some comments plz..

thanks.

ZY.
 

rfid chip 50 ohm

yaa for measuring antenna in PET I think you need Wafer probe or similar stuff, you cant solder cable and all to silver ink.

attached is the doc, just some basic, still the real problem exist....:D
 

Yes problem is still alive. Because of determining experimantal VSWR or impedance etc problem; i said use a simulation tool and trust it. that is better.(Do you think that tag manufacturer is determining their measurement one by one??)
in real life they are using some printed antenna over some thicker subrates than pet. Simulating it. measuring it. and after succesfull results they are changing subrate and simulating finally. There may be some other ways to measure VSWR too.(such as building your own VSWR meter) But hard to implement.(For instance: you may connect 50 ohm circuit to the asic pads on antenna(use surface mount equipment on tag side with suitable welding). and after that you send signal from a specific distance. And measure. repeat operation with any antenna having known measurement. And compare the results!! Very hard way.. i ll still simulate...:)
 

hi zirtapoz
as what you said,in real it is impossible to measure the antenna one by one..
but now my problem is a lab work.
I need a way to prove my simulation is right or not... i mean.. i dont know if the simulation is accurate without the comparation between measured result and simulated...
do you mean measure the FR4 antenna instead of PET one to testify the simulation work?

thanks..
ZY.
 

yes. maybe. or other type of subrates. All ll work, or if i m not right ;Maxell had to be fabulist...:)
 

hi guys
i have this problem too i make an rfid passive tag in uhf band
my antenna is a replied dipole and i don't make an measurement of impedance caus eil dipole an my merasure is wrong
have u any idfeas pls
regards
 

how does one see the operating frequency for a near field uhf small loop tag? or how can I check whether my simulation is correct? My supervisor told me that return loss is not application here as the radiation resistance is too small. I have simply draw out a small loop antenna but I do not know how to proceed from there. The results are a mess.
 

Hi,

yes that is correct even in simulation simulating with a 50 ohm port wont give you the correct measure of S11.

If you have a tag tester , like Ni's PXIe-1062Q Put your tag on it and sweep the frequency. It will back scatter more at the resonat frequency.

I have tried measuring using a probe made using semirigid cable and got near accurate measurement of resonant frequency. may not be correct always.
 

I have not fabricated my tag out yet. I have to come out with more simulation and explanation on the near field effect. As for my small loop antenna for near field uhf, I cant measure the return loss to see my frequency. I was told to look at my current distribution but no further details were given after then. Anyone could tell me how by looking at the current distribution i can explain the nature of my antenna?
 

hi all ineed avery serious help in this topic i need to design a digital system tracking and controlling,,so for this i opted rfid ,,,i need vlsi design of both rfid tag and the reader and also inlay programming for tag ic chip ,,and also some basic information about the interface between the rader and tag plzzzz help asoon as possible
 

CST HELP

The port I use has impedance 150 ohms, and I have frequency resonant at 865.5Mhz. But if I change port impedance value, it miss resonant.
I can't change port impedance to complex value 10-245j!. The RFID chip has impedance 10-245j at resonant frequency.

Plz help to match between antenna and IC?
 

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